1. Technical Field
The present invention relates to a communication system, a main communication device of the communication system, and an auxiliary communication device of the communication system
2. Related Art
Various communication systems for executing data communication and voice communication using a prescribed frequency band are known and used today. In such communication systems, the same frequency band can be used for both data communication and voice communication. For example, a 2.4 GHz band, which is called an “ISM (Industry Science Medical) band”, is used for both wireless LANs (Local Area Networks) for the purpose of data communication and DCL (Digital CordLess) telephones for the purpose of voice communication.
For the wireless LANs and DCL telephones, multiple channels obtained by segmenting a prescribed frequency band are assigned separately to the two communication methods. In the following description, a channel used for wireless LANs will be referred to as a “WLAN channel” while a channel used for DCL telephones will be referred to as a “DCL channel” in order to discriminate between the channels for the two communication methods.
In a wireless LAN, a frequency band from 2.4 GHz to 2.5 GHz is segmented into fourteen WLAN channels (wch1-wch14). Among the fourteen WLAN channels, a WLAN channel assigned once is used continuously. Incidentally, the wireless communication in a wireless LAN is carried out by executing the spread spectrum modulation to the data to be transmitted while continuously using the one WLAN channel already assigned.
On the other hand, for DCL telephones, the frequency band from 2.4 GHz to 2.5 GHz is segmented into eighty-nine DCL channels (dch1-dch89). Among a prescribed number of DCL channels (e.g. forty-five DCL channels) previously selected from the eighty-nine DCL channels, a DCL channel to be used is successively switched (hopping) at prescribed periods called “hopping periods” (e.g. 1/100 seconds). As above, the wireless communication by DCL telephones is carried out by successively switching the DCL channel at prescribed periods.
As explained above, the frequency band from 2.4 GHz to 2.5 GHz is segmented into eighty-nine DCL channels for DCL telephones whereas the same frequency band is segmented into fourteen WLAN channels for wireless LANs. Thus, the frequency bandwidth of a WLAN channel used for a wireless LAN is approximately 20 MHz, which is far wider than that of a DCL channel used for DCL telephones (less than 1 MHz). For this reason, the wireless LAN communication (wireless communication via a wireless LAN), enabling a higher data transfer rate (per unit time) compared to the DCL wireless communication (wireless communication by DCL telephones), is used a lot for data communication.
A technology (wireless communication system) for executing data communication by the wireless LAN communication while also executing voice communication by the DCL wireless communication is widely known.